The present invention relates to a method for controlling an electrohydraulically operated infinitely variable transmission of a driven motor vehicle.
Conventional methods for controlling infinitely variable motor vehicle transmissions adjust the ratio of the transmission via a characteristic control curve automatically at least as a function of the position of the throttle valve and the rotational speed of the engine. In this case, the characteristic control curve is designed according to the following criteria: It must permit an operation that is either as economical as possible or an operation that is as power-oriented as possible.
In this regard, it has become known from Japanese Patent Document JP-OS 59-217050 to control an infinitely variable transmission on the basis of characteristic diagrams which are selected corresponding to a driving situation. As a result, it is achieved that the driver's requirements with respect to a consumption--favorable driving and driving performances are taken into account.
However, the internal-combustion engines which, as a rule, are used for driving the motor vehicle do not permit both criteria to be met at the same time. Frequently, there can therefore only be a compromise between two extremes because a purely consumption-optimized characteristic control curve does not offer sufficient safety reserves in critical traffic situations, and the fuel consumption is too high in the case of a power-optimized characteristic control curve.
Another possibility is the manual change-over between consumption-optimized and power-optimized characteristic control curves. However, this case, the driver must first operate a change-over switch before the corresponding switching program is made available to him. Moreover, only two extreme alternatives are offered to the driver which, however, permit only either a consumption-oriented or a power-oriented vehicle handling.
From German Patent Documents DE-PS 33 41 652 and DE 39 22 051 A1, it has become known in this context to automate this manual change-over. For this purpose, at least one accelerator pedal or throttle valve signal which is proportional to the position of the accelerator pedal is scanned and stored. By means of the scanned value, signal values which were detected earlier and were stored are continuously updated and a driving activity is calculated which evaluates a driver's driving style or his actions with respect to the control of the motor vehicle which are the result of a traffic situation. This driving activity will then be used for selectively influencing limit values for shifting decisions or for the selection of characteristic shifting curves in such a manner that the transition from the consumption-optimized shifting program to the power-optimized shifting program takes place continuously or in steps.
By means of the described devices and methods, it is therefore possible to simulate the driver's driving style by detecting a quantity which is representative of this style. However, the methods which are used as the basis can be applied to infinitely variable transmissions only to a limited degree because the latter have substantially different requirements and possibilities with respect to the control. Thus, infinitely variable transmissions, for example, permit a larger spread of the transmission ratios and allow an operation of the internal-combustion engine in virtually any possible and useful operating point.
It is therefore an object of the invention to provide a method for controlling an infinitely variable motor vehicle transmission by means of which a motor vehicle equipped with this type of transmission can be operated as optimally as possible and which is automatically adjusted to a driving style of the driver or to his actions with respect to the control of the motor vehicle caused by the traffic situation.
The principal advantages of the invention are that a method is provided for controlling an infinitely variable motor vehicle transmission which, based on a control method that is as consumption-optimal as possible, is dynamically adapted to the driver's vehicle handling, without the requirement of operating additional operating elements.
This is mainly achieved by the fact that the ratio of the transmission is automatically adjusted indirectly via characteristic control curves at least as a function of the position of the power control element, such as a throttle valve or an accelerator pedal and of the rotational speed of the engine of the internal-combustion engine. In this case, the characteristic control curve is selected from a family of several characteristic control curves corresponding to a driving activity which evaluates the driver's driving style or his actions with respect to the control of the motor vehicle which are the result of a traffic situation.
The characteristic control curves cover at least in steps the range between a characteristic control curve which permits the consumption-optimized operation of the motor vehicle and a characteristic control curve which permits the power-optimized operation of the motor vehicle.
Advantageously, the transmission ratio is adjusted in such a manner that the rotational speed of the engine follows a desired rotational engine speed value which is assigned via the momentarily selected characteristic control curve to a momentary value of the throttle valve position.
In a lower value range of the throttle valve position, the characteristic control curves preferably have a progressive course which changes into a degressive course in a medium range.
On the one hand, this results in a control action of the transmission which is optimally adapted to the driver's driving style or to his actions caused by a traffic situation, and, on the other hand, the control method permits, with respect to the overall vehicle, virtually the adjustment of a desired power value by the driver and its control via the internal-combustion engine--transmission system.